The present invention relates to ceiling fans, and, in particular, to a one-piece arm and blade unit for a ceiling fan.
Ceiling fans include a motor disposed in a housing and a plurality of arm and blade assemblies connected to the motor for rotation. Each arm and blade assembly is typically manufactured as two pieces which are then permanently joined. One reason for such a two-piece design is that the blades are typically made out of a lightweight material such as a lightweight wood or plastic, in order to reduce the overall weight of the fan, while the arms must be sufficiently rigid and strong to withstand the various stresses from the fan operation.
These stresses are numerous and severe and, as such, limit the design possibilities of the arm and blade assemblies. For example, a centrifugal stress acts on the arm and blade assembly which can cause radial separation of the blades from the motor portion due to the centrifugal weight of the blades which increases as the fan speed increases. Another stress is caused by the aerodynamics of the fan blades as they rotate through the air. More specifically, and assuming that the fan is rotating in a direction to blow air downwardly, the air stream passing over the blade surface creates a "lift stress" which can cause each blade to bend toward the ground as the fan is operated. Similarly, a reactive stress results from the fan blades thrusting air rearwardly behind them toward the ceiling. Also, streams of air from a vent, or the like, passing through or into a portion of the normal air path through the fan, increases lift and reactive stresses on the individual fan blades as they pass through the airstream pathway. Further, a twist stress, caused primarily by centrifugal forces, may cause each fan blade to tend to twist about its longitudinal axis; while harmonic, or noise, stress can set up standing vibrational or oscillatory waves in the fan. Therefore, if the arm and blade assemblies of the fan are not designed properly, the fan will vibrate, rock and shake during use.
Although it would be desirable, from at least a manufacturing efficiency standpoint, to manufacture a one-piece arm and blade unit, it is very difficult due to the facts that the arm and blade assemblies must be relatively light in weight and must withstand the above stresses. Therefore, arm and blade assemblies constructed of the lightweight materials mentioned above are not ordinarily strong and rigid enough to withstand the stresses. While new and stronger plastics or polyresins are being developed, one-piece plastic fan arm and blade assemblies fabricated from these plastics are relatively expensive and still often cannot withstand many of the stresses mentioned above.
Therefore, what is needed is a one-piece arm and blade unit for a ceiling fan that is rigid enough to withstand the above stresses yet is relatively light in weight and inexpensive to manufacture.